1. Field of the Invention
The present invention relates to fastening systems for flexible plastic sheeting, and more particularly to a system for fastening multiple layers of plastic sheeting along an edge thereof.
2. Background of the Invention
The use of polyethylene film and other thin pliable plastic films is widespread, especially in the greenhouse industry. It is common to build a greenhouse framework from metal or the like and to temporarily cover the framework with polyethylene film or other type of plastic sheeting. It is desired to install and remove such film frequently; for example, in some instances transparent film is desired while at another time opaque film is necessary. The film is subjected to various forces such as wind, pressurization of the greenhouse, and hot air forming between layers of film.
Another requirement is that of having multiple layers of film to produce insulating air spaces to retain heat within the greenhouse. Thus, there is a need for a simple, low cost film fastening system in which various thicknesses or plies of plastic film can be quickly installed, which will be securely held in place when subjected to forces and which can be easily removed when desired. In addition, the system needs to provide for multiple layers of film when required.
There are a number of prior art patents which address this problem; for example, the following U.S. Patents disclose plastic film gripping or holding systems: Daniels U.S. Pat. No. 3,225,407; Blumfield U.S. Pat. Nos. 3,805,873 and 3,987,835; Curry U.S. Pat. No. 3,999,258; Connelly U.S. Pat. No. 4,103,401; Derrick et al U.S. Pat No. 4,231,141, Blumfield U.S. Pat. No. 4,267,876; and Blumfield et al U.S. Pat. No. 4,472,862. The majority of these patents show a rigid, channel member and a resilient core member which may be snapped into the channel member. Such holders depend upon the resiliency of the core member to hold the sheet in place. When exposed to the atmosphere, the resilient members eventually tend to deteriorate and lose their resiliency and therefore do not firmly grip the sheet plastic. The prior art plastic sheet holders are also deficient in that they do not provide for multiple layers of film or are limited to a specific thickness of sheets.